I know that there are a category of heroes that are junglers and can do it very well, but as I was learning one of the newly released heroes (Medusa), I discovered that under specific circumstances, she can jungle the ancients group as soon as the game starts.

This is done by chopping down some specific trees with the quelling blade, and using an observer ward to grant vision. (example videos: #1, #2).

What other heroes not listed as a jungler can jungle using very specific items or tactics?

I'm not sure how well this question can be answered. In theory, practically any hero can jungle, it's mostly a matter of determining how well they actually succeed at doing so. How are you going to measure that here?
–
FAEJan 30 '13 at 23:54

1

@FAE well, jungling effectively means you aren't blowing all your initial gold on potions and running back to the fountain to heal. You have to be able to get a reasonable amount of gold and keep pace with other lane heros level wise
–
z 'Jan 31 '13 at 0:11

The problem with all of these heroes is that it's very easy to shut them down and steal their farm, and it's very conspicuous as none of the heroes are viable roamers or gankers early in the game. Jungling usually means doing so from level 1 and keeping pace somewhere between a dual laner and a solo in terms of experience.

To be complete, the following heroes can jungle (traditionally) reasonably well:

Axe

Batrider

Chen

Doom

Dark Seer

Enchantress

Enigma

Legion Commander

Lifestealer

Lone Druid

Lycanthrope

Nature's Prophet

Ursa

The following heroes can jungle if it's absolutely needed but they're slow at doing so and thus probably shouldn't:

KotL can't really do it until level 2 because he's out of mana after 2 nukes. Ditto Juggernaut and QoP, they need to courier so much regen that it's not even close to worthwhile.
–
DecencyJan 31 '13 at 16:35

Usually, junglers like Nature's Prophetand Lycan can be very much help with ganking. They can roam while their spawns are active and can be good at being first in every neutral creeping.Nature's teleport/ult and Lycan's ult are suprisingly good combination of surprise ganks and intimidation to enemy heroes. If you want a jungle that not only farm and gank, but also become a late game initiator, try Barathrum. His charge and ult is the best initiator in teamfights because he can zone out the most fed up heroes with no escape abilities such as Sniper, Tinker, Lanaya, and other Intelligence-type heroes that you can engage.